The present invention pertains to check valves and, more specifically, to those check valves in which the valve body, typically formed of metal, has its interior lined with another material. It has become particularly popular to line such check valve bodies with suitable polymeric materials, although certain aspects of the invention may likewise be applicable to valve bodies and liners formed, for example, of two different metals. The respective materials of the valve body and liner often have different thermal properties and, more particularly, much different coefficients of thermal expansion.
In many instances, it is necessary, or at least desirable, to provide an accurate alignment and guiding mechanism for the valve element, e.g. so that it will reciprocate in a straight longitudinal path on the centerline of the valve seat and will remain properly angularly oriented with respect to that seat. A fairly conventional approach is illustrated in U.S. Pat. No. 2,912,000 to Green and also in U.S. Pat. No. 2,071,391 to Crowell. Each of these patents illustrates a valve body in which a more or less conventional spider structure is provided for sliding engagement with the valve stem. The legs of the spider are joined at their inner ends by a continuous ring. If the valve body, including the spider, is lined, e.g. with a polymeric material, and then subjected to thermal changes in use, the portion of the liner lining the inner ring of the spider structure can shrink upon and bind the valve stem, thereby foiling its own purpose of facilitating proper valve element movement. Such spiders are also typically short in longitudinal dimension and, thus, do not adequately prevent cocking.
U.S. Pat. No. 3,498,315 to Graves et al illustrates a different approach in which the valve element does not include a guided stem, but rather, is a simple ball-type element. This arrangement is undesirable, for example, in that it is impossible to guide a ball-type element as surely and accurately as a stemmed element. Thus, gravity may interfere with proper seating of the ball on its seat. Some limited guidance is provided by vein-like structures formed on the interior of the liner, but these offer only incomplete guidance and, in any event, make the liner more expensive and difficult to manufacture. U.S. Pat. No. 4,224,961 to Schnabel illustrates a similar scheme, except that separate plastic inserts are provided between the liner and the valve body to help define the guide structures.
U.S. Pat. No. 3,540,472 to Brady suggests the formation of the entire valve body, including its internal guide structure, from a single material, namely a suitable plastic. However, for many applications, it is necessary, or at least desirable, that the outer major portion of the valve body be formed of metal, with only a relatively small layer of liner material on the interior. U.S. Pat. No. 3,552,426 to Hester et al and U.S. Pat. No. 4,274,436 to Smith generally disclose plastic-to-metal interlock formations for valves, but do not address the specific problem of interlocking a liner with guide formations of a valve body.